This invention relates to an exhaust port control system for a two stroke engine and more particularly to an improved, simplified and easily manufactured arrangement for reducing the compression ratio of a two stroke engine under certain running conditions.
It has been well known to provide some structure for reducing the compression ratio of a two cycle engine for a variety of purposes. This can be done either for starting or so as to limit the compression pressure in a diesel engine under high load running. A variety of decompression devices have been provided for these various purposes. One type of decompression device that has been proposed and which is usable in reducing the compression ratio of a diesel two cycle engine under high load operation employs a supplemental exhaust port that opens into the cylinder bore at a level so that it will open before the main exhaust port. An exhaust control valve is provided in the supplemental exhaust port so that the supplemental exhaust port can be closed under running conditions when its use is not necessary. For example, this type of control valve is opened under high load running so as to reduce the compression ratio and protect the life of the engine.
In the devices of this type which have been previously proposed, the supplemental exhaust port intercepts the main exhaust port so that the exhaust gases from the supplemental port can pass into the common exhaust manifold of the main exhaust system. However, this type of arrangement results in the provision of a complicated passageway for the supplemental exhaust port and one which can offer high flow resistance and, accordingly, deteriorate the performance.
It is, therefore, a principal object of this invention to provide an improved, simplified and lost cost exhaust port control system for a two stroke engine.
It is a further object of this invention to provide an improved and simplified supplemental exhaust port system for a two stroke engine that can be easily and conveniently manufactured and which will not detract from the performance.
It is a further object of this invention to provide a supplemental exhaust port system for a two stroke engine wherein the supplemental exhaust port will offer a low flow resistance and high efficiency and can be inexpensively manufactured.